The present invention is concerned with differential pressure sensing apparatus.
A well known form of differential pressure sensor comprises a body in which there is mounted a diaphram which separates two pressure chambers within the body. The pressure difference to be measured is applied across the diaphragm usually by supplying a pressure transmitting fluid at appropriate pressures to each pressure chamber. The pressure difference across the diaphragm then distorts or strains the diaphragm and the amount of distortion or strain is measured to provide an indication of the pressure difference. Commonly, the diaphragm is planar in the absence of a pressure difference across it. In one known arrangement, the displacement of the diaphragm to one side or the other of the rest plane is monitored and used to provide an indication of the differential pressure. A commonly used technique for monitoring the displacement of the diaphragm is the capacitative technique in which the diaphragm constitutes a movable plate in a capacitor. The displacement of the diaphragm can be monitored by measuring variations in the capacitance of the capacitor. Commonly, a fixed capacitor plate is provided on each side of the diaphragm and the capacitances of both capacitors formed thereby are monitored and used to provide an indication of the differential pressure.